1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to supporting multiple wireless communication protocols within a wireless local area network.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies them. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is further known, the standard to which a wireless communication device is compliant within a wireless communication system may vary. For instance, as the IEEE 802.11 specification has evolved from IEEE 802.11 to IEEE 802.11b to IEEE 802.11a and to IEEE 802.11g, wireless communication devices that are compliant with IEEE 802.11b may exist in the same wireless local area network (WLAN) as IEEE 802.11g compliant wireless communication devices. As another example, IEEE 802.11a compliant wireless communication devices may reside in the same WLAN as IEEE 802.11g compliant wireless communication devices. When legacy devices (i.e., those compliant with an earlier version of a standard) reside in the same WLAN as devices compliant with later versions of the standard, a mechanism is employed to insure that legacy devices know when the newer version devices are utilizing the wireless channel as to avoid a collision.
For instance, backward compatibility with legacy devices has been enabled exclusively at either the physical (PHY) layer (in the case of IEEE 802.11b) or the Media-Specific Access Control (MAC) layer (in the case of 802.11g). At the PHY layer, backward compatibility is achieved by re-using the PHY preamble from a previous standard. In this instance, legacy devices will decode the preamble portion of all signals, which provides sufficient information for determining that the wireless channel is in use for a specific period of time, thereby avoid collisions even though the legacy devices cannot fully demodulate and/or decode the transmitted frame(s).
At the MAC layer, backward compatibility with legacy devices is enabled by forcing devices that are compliant with a newer version of the standard to transmit special frames using modes or data rates that are employed by legacy devices. For example, the newer devices may transmit Clear to Send/Ready to Send (CTS/RTS) exchange frames and/or CTS to self frames as are employed in IEEE 802.11g. These special frames contain information that sets the NAV (network allocation vector) of legacy devices such that these devices know when the wireless channel is in use by newer stations.
Both of the existing mechanisms for backward compatibility suffer from a performance loss relative to that which can be achieved without backward compatibility and are used independently of each other.
Therefore, a need exists for a method and apparatus that enables multiple protocols to be supported within a wireless communication system, including wireless local area networks, for MIMO communications.